When to Convert HDR to Black and White
One option to create black-and-white high dynamic range (HDR) images is to convert your color photos to black and white before using them to generate the HDR image. You have two options to choose from if this is the direction you want to go in:
Convert during Raw conversion.
Convert during tone mapping.
If you’re wondering what order to do things in; that is, should you convert to black and white before or after you sharpen? Before or after you increase contrast? Before or after you transform, resize, reshape? Here’s one good strategy: Create the best color image you can, complete with sharpening, noise reduction, cloning, and any other adjustments you want to make. Then convert to black and white.
This way, if you decide you don’t like how the black-and-white image turned out, you don’t have to do everything all over again. You can just pick up the finished color image and go back to the black-and-white drawing board.
The obsession over creating the perfect workflow is often overrated from a quality perspective. Use the workflow that preserves quality, but also time.
You may also (depending on the options of your HDR application) convert an HDR image to black and white while you tone map. Conversion using a standard color saturation control is very simple. Reduce it to 0 and you’re done, as shown in this figure.
Photomatix Pro has a few saturation options (different controls for highlights and shadows), but overall color intensity is controlled by the Color Saturation setting. Setting it to 0 turns the image to grayscale.
Try tone mapping the color image until you reach the effect you’re after, and then reduce saturation to 0 to convert it to black and white. Alternatively, reduce Color Saturation to 0 first; then manipulate the other settings to achieve the best look for the image.
The downside to converting color HDR images to black and white at this stage is generally a loss of control. Color saturation settings are simple, and you have very few, if any, options to manage the tones you want.